JP2022143342A - X-ray photographing device and x-ray photographing method - Google Patents

Abstract

To provide an X-ray photographing device with which it is possible to shorten a photographing time while detecting an X-ray greater than or equal to a reference value needed for imaging in both an out-of-subject area and a subject area.SOLUTION: This X-ray photographing device 100 comprises an X-ray source 1, an X-ray detection unit 2 for detecting the X-ray radiated from the X-ray source 1, and a control unit 4 for controlling a condition for X-ray photographing of a subject 110 by the X-ray source 1 and the X-ray detection unit 2. The control unit 4 is constituted so as to set a first X-ray photographing condition under which the out-of-subject area of the X-ray detection unit 2 can detect an X-ray greater than or equal to a reference value needed for imaging in first X-ray photographing and set a second X-ray photographing condition under which the subject area of the X-ray detection unit 2 can detect an X-ray greater than or equal to the reference value in second X-ray photographing which is performed after the first X-ray photographing.SELECTED DRAWING: Figure 4

Description

The present invention relates to an X-ray imaging apparatus and an X-ray imaging method, and more particularly to an X-ray imaging apparatus and an X-ray imaging method for detecting X-rays.

2. Description of the Related Art Conventionally, an X-ray imaging apparatus that detects X-rays is known (see Patent Document 1, for example).

The aforementioned Patent Document 1 discloses an X-ray CT apparatus (X-ray imaging apparatus) that detects X-rays. This X-ray CT apparatus is configured such that X-rays emitted from an X-ray tube are condensed through a collimator and directed to an X-ray detector. In addition, this X-ray CT apparatus has an X-ray tube, a collimator, and an X-ray detector arranged in a space sandwiched between the X-ray tube, the collimator, and the X-ray detector, with the body axis of the subject as the central axis. , are configured to rotate together. Also, this X-ray CT apparatus is configured to perform X-ray imaging of a subject while the X-ray tube, collimator, and X-ray detector are integrally rotated.

JP-A-2005-237779

Here, in the conventional X-ray imaging apparatus, the object does not absorb the X-rays in the region of the X-ray detector where the X-rays passing through the space where the object does not exist (referred to as the outside-object region) are detected. Therefore, the amount of X-rays detected per unit time is increased. In addition, in the area of the X-ray detector where the X-rays passing through the space where the subject exists (referred to as the subject area), the detected amount of X-rays per unit time increases according to the absorption of the X-rays by the subject. become smaller. Also, in the X-ray detector, the amount of X-rays that can be detected per unit time is limited. Therefore, X-ray imaging is performed so that the non-subject area where the detected amount of X-rays is greater falls within the range of the above restrictions.

In this case, an attempt to detect X-rays of a reference value or more required for imaging in an object region where the amount of detected X-rays per unit time is smaller than that in the non-object region has the disadvantage of lengthening the imaging time. On the other hand, if the imaging time is long, X-rays exceeding the reference value necessary for imaging may be detected in an area outside the subject where the amount of detected X-rays per unit time is large.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and one object of the present invention is to detect X-rays of a reference value or more necessary for imaging in both the area outside the subject and the area of the subject. An object of the present invention is to provide an X-ray imaging apparatus and an X-ray imaging method capable of shortening the imaging time.

In order to achieve the above object, an X-ray imaging apparatus according to a first aspect of the present invention comprises an X-ray source, an X-ray detector that detects X-rays emitted from the X-ray source, an X-ray source and an X-ray detector. a control unit for controlling conditions for X-ray imaging of a subject by the ray detection unit, wherein the control unit controls, in the first X-ray imaging, that the area outside the subject of the X-ray detection unit is equal to or greater than a reference value necessary for imaging. is set, and in the second X-ray imaging performed after the first X-ray imaging, the object region of the X-ray detection unit is set to the second X-ray imaging condition capable of detecting X-rays equal to or greater than the reference value. It is configured to set line imaging conditions.

In order to achieve the above object, the X-ray imaging method according to the second aspect of the present invention includes the step of detecting X-rays with an X-ray detector, and a step of performing a first X-ray imaging under a first X-ray imaging condition capable of detecting X-rays of a required reference value or more; and performing a second X-ray imaging after the first X-ray imaging under imaging conditions.

According to the X-ray imaging apparatus in the first aspect and the X-ray imaging method in the second aspect, by performing X-ray imaging a plurality of times under suitable conditions, imaging is performed both in the area outside the subject and in the subject area. It is possible to shorten the imaging time while detecting X-rays above the reference value necessary for the detection.

1 is a schematic diagram showing the configuration of an X-ray imaging apparatus according to a first embodiment; FIG. 4 is a schematic diagram for explaining detection of X-rays by an X-ray detection unit of the X-ray imaging apparatus according to the first embodiment; FIG. 4 is a schematic graph for explaining the distribution of X-ray photon counts in an X-ray detection unit; 4 is a schematic diagram for explaining first X-ray imaging and second X-ray imaging of the X-ray imaging apparatus according to the first embodiment; FIG. 4 is a schematic graph showing the result of first X-ray imaging by the X-ray imaging apparatus according to the first embodiment; 7 is a schematic graph for explaining the effect of shortening the imaging time; 5 is a schematic graph showing the distribution of count numbers before reconstruction of the X-ray imaging apparatus according to the first embodiment; 4 is a schematic graph showing the distribution of count numbers after reconstruction of the X-ray imaging apparatus according to the first embodiment; It is a graph for explaining a simulation result. It is a figure for demonstrating a simulation result. 4 is a flowchart for explaining X-ray imaging processing of the X-ray imaging apparatus according to the first embodiment; FIG. 6 is a schematic diagram showing the configuration of an X-ray imaging apparatus according to a second embodiment; FIG. 10 is a schematic diagram for explaining first X-ray imaging and second X-ray imaging of the X-ray imaging apparatus according to the second embodiment; FIG. 4 is a schematic graph for explaining the distribution of X-ray detection values in an integral X-ray detection unit; FIG.

An embodiment embodying the present invention will be described below with reference to the drawings.

[First embodiment]
(Configuration of X-ray imaging device)
A configuration of an X-ray imaging apparatus 100 according to a first embodiment of the present invention will be described with reference to FIGS. 1 to 7. FIG.

As shown in FIG. 1, the X-ray imaging apparatus 100 is a photon-counting type X-ray imaging apparatus that generates an image of the inside of a subject 110 using X-ray photons that have passed through the subject 110 . Specifically, the X-ray imaging apparatus 100 is a PCCT (Photon Counting Computed Tomography) apparatus. Further, the X-ray imaging apparatus 100 is configured to be able to perform material discrimination by utilizing the fact that the energy value characteristics of the X-ray photons transmitted through the subject 110 differ from material to material.

The X-ray imaging apparatus 100 includes an X-ray source 1 , an X-ray detector 2 , a rotating stage 3 and a controller 4 .

The X-ray source 1 is configured to irradiate an object 110 with X-rays. The X-ray source 1 includes an X-ray tube, and is configured to generate X-rays and irradiate the X-ray detection unit 2 with the generated X-rays when a high voltage is applied. . Also, the X-ray source 1 is configured to be able to change the tube current under the control of the controller 4 .

The X-ray detection unit 2 is a photon counting type X-ray detection unit. The X-ray detector 2 is configured to detect X-ray photons emitted from the X-ray source 1 . The X-ray detector 2 is also configured to convert detected X-ray photons into electric signals and output the converted electric signals. Specifically, the X-ray detector 2 is configured to output electrical signals corresponding to X-ray photons so that the number of X-ray photons for each energy value can be counted. there is This makes it possible to count the number of X-ray photons per energy range (so-called bin).

The X-ray detection unit 2 also includes a plurality of detection elements that convert X-ray photons into electrical signals. As the detection element, for example, a direct conversion semiconductor element that directly converts X-ray photons into electric signals can be employed. As such a semiconductor element, for example, a cadmium tellurium-based semiconductor element can be cited. In addition, the detection element includes, for example, a scintillator that converts X-ray photons into light and a photodiode that converts light into electrical signals, and indirect conversion type detection that indirectly converts X-ray photons into electrical signals. elements may be employed.

The rotating stage 3 is configured to rotate the subject 110 . The rotating stage 3 includes a mounting table for mounting the object 110 and a drive unit such as a motor for rotating the mounting table. The rotating stage 3 is configured to rotate under the control of the control section 4 . By rotating the object 110 with the rotating stage 3 , the object 110 can be rotated with respect to the imaging system including the X-ray source 1 and the X-ray detector 2 . As a result, X-ray imaging can be performed while changing the X-ray irradiation position on the object 110 .

The control section 4 is configured to control each section of the X-ray imaging apparatus 100 . The control unit 4 includes a processor such as a CPU (Central Processing Unit) and a memory. Further, the control unit 4 functions as an image processing unit that performs data processing regarding images. Specifically, the control unit 4 is configured to acquire a plurality of sinogram image data corresponding to a plurality of energy ranges (a plurality of bins) based on the detection result of X-ray photons by the X-ray detection unit 2. ing. The sinogram image data is image data obtained by two-dimensionally arranging the detection results of X-ray photons by the X-ray detection unit 2 according to the number of the detection element (detector number) and the rotation angle.

The control unit 4 is configured to acquire reconstructed image data by performing reconstruction processing such as FBP (Filtered Back Projection) on the sinogram image data. Note that reconstructed image data can be obtained for each sinogram image data. That is, it is possible to obtain a plurality of reconstructed image data based on a plurality of sinogram image data. Further, the control unit 4 is configured to perform material discrimination of the object 110 based on a plurality of pieces of reconstructed image data.

(Detection of X-rays by X-ray detector)
Next, detection of X-rays by the X-ray detector 2 will be described with reference to FIGS. 2 and 3. FIG.

As shown in FIG. 2, the X-ray source 1 is configured to irradiate a range including a subject 110 and the outside of the subject 110 with X-rays. The X-ray detection unit 2 is configured to detect X-rays that have passed through the subject 110 and X-rays that have passed outside the subject 110 . Therefore, the X-ray detection unit 2 includes an object area for detecting X-rays that have passed through the object 110 and an outside-object area for detecting X-rays that have passed outside the object 110 . Note that the subject area and the non-subject area change depending on the size and shape of the subject 110 . In addition, since the subject 110 does not absorb the X-rays in the area outside the subject, the amount of X-rays detected per unit time increases. Also, in the subject area, the subject 110 absorbs X-rays, so the amount of X-rays detected per unit time is reduced.

FIG. 3 shows a graph of the distribution of the number of counts of X-ray photons in the X-ray detection unit 2 when the cylindrical subject 110 is imaged. In the graph of FIG. 3, the vertical axis indicates the number of X-ray photons counted, and the horizontal axis indicates the position (pixel) of the X-ray detection unit 2 in the X-axis direction. In the graph of FIG. 3 , the X-ray photon count is large at both ends in the X-axis direction corresponding to the non-subject area, and the X-ray photon count is small at the center in the X-axis direction corresponding to the subject area. It's becoming A graph similar to the graph shown in FIG. 3 is also obtained when the vertical axis is the X-ray photon count rate (the number of X-ray photons counted per unit time). Therefore, the X-ray photon count rate is high at both ends in the X-axis direction corresponding to the non-subject area, and the X-ray photon count rate is low at the center portion in the X-axis direction corresponding to the subject area.

The X-ray detector 2 also has an upper limit for the number of counts of X-ray photons that can be detected per unit time (that is, an upper limit for the counting rate). When the X-ray detection unit 2 detects X-ray photons exceeding the upper limit, a plurality of X-ray photons are detected as one X-ray photon, so a normal X-ray photon count cannot be obtained. . Therefore, it is necessary to detect X-ray photons below the upper limit for both the subject region and the non-subject region. For this reason, when X-ray imaging is performed only once, X-ray imaging is performed so that the count rate of the area outside the subject where the count rate of X-ray photons is high does not exceed the upper limit.

In this case, the X-ray photon count rate in the subject area is lower than in the area outside the subject, so the imaging time will be longer in order to detect X-rays above the reference value necessary for imaging in the subject area. I have an inconvenience. Also, in order to shorten the imaging time, it is conceivable to increase the X-ray photon count rate in the object region by increasing the tube current of the X-ray source 1, but simply increasing the tube current of the X-ray source 1 does not There is also the inconvenience that the count rate for the area outside the subject exceeds the upper limit value if only the number is set. In addition, since the count rate of X-ray photons in the area outside the subject is higher than that in the subject area, if X-rays exceeding the reference value required for imaging in the subject area are detected, the area outside the subject will exceed the threshold required for imaging. There is also the disadvantage that X-rays far in excess of the value are detected. For these reasons, it is desired to shorten the imaging time while detecting X-rays of a reference value or more necessary for imaging in both the non-subject region and the subject region.

(first X-ray and second X-ray)
Therefore, in the first embodiment, as shown in FIG. 4, the control unit 4 is configured to control the conditions for X-ray imaging of the object 110 by the X-ray source 1 and the X-ray detection unit 2. FIG. Specifically, in the first X-ray imaging, the control unit 4 sets the first X-ray imaging conditions under which the area outside the object of the X-ray detection unit 2 can detect X-rays of a reference value or more necessary for imaging. In the second X-ray imaging performed after the first X-ray imaging, the object region of the X-ray detector 2 is configured to set a second X-ray imaging condition under which X-rays equal to or greater than the reference value can be detected. That is, the X-ray imaging apparatus 100 performs the first X-ray imaging under the first X-ray imaging conditions in which the X-ray detection unit 2 can detect X-rays of a reference value or more in the area outside the subject, and the X-ray detection unit 2 The object region is configured to perform the second X-ray imaging under the second X-ray imaging conditions under which X-rays equal to or greater than the reference value can be detected.

More specifically, in the first X-ray imaging, the control unit 4 sets the first X-ray imaging conditions under which the area outside the object of the X-ray detection unit 2 can detect X-ray photons equal to or greater than the reference count required for imaging. is set, and in the second X-ray imaging, the object region of the X-ray detection unit 2 is configured to set a second X-ray imaging condition under which X-ray photons equal to or larger than the reference count can be detected. That is, the X-ray imaging apparatus 100 performs the first X-ray imaging under the first X-ray imaging conditions under which the X-ray detection unit 2 can detect X-ray photons equal to or greater than the reference count number, and the X-ray detection unit 2 subject regions are configured to perform second X-ray imaging under second X-ray imaging conditions under which X-ray photons equal to or greater than the reference count can be detected. Note that the reference count number is the minimum count number required to obtain a reconstructed image with sufficient image quality. The reference count number is obtained in advance through experiments or the like.

Further, in the first embodiment, the control unit 4 is configured to change the X-ray imaging conditions by controlling the tube current of the X-ray source 1 . Specifically, the control unit 4 sets the first tube current to the X-ray source 1 in the first X-ray imaging, and sets the second tube current larger than the first tube current in the second X-ray imaging. It is configured to be set for the source 1 .

Further, in the first embodiment, the control unit 4 controls that the X-rays detected by the extra-subject area of the X-ray detection unit 2 do not exceed the detection limit (counting rate limit) of the X-ray detection unit 2 in the first X-ray imaging. The first tube current is set for the X-ray source 1, and in the second X-ray imaging, the X-rays detected by the area outside the object of the X-ray detection unit 2 exceed the detection limit (counting rate limit) of the X-ray detection unit 2. X-ray source 1 is set to a second tube current that exceeds the detection limit (counting rate limit) of X-ray detection unit 2 and X-rays detected by the object region of X-ray detection unit 2 do not exceed the detection limit (count rate limit) of X-ray detection unit 2. It is configured. Specifically, in the first X-ray imaging, the control unit 4 controls the X-rays detected by the extra-subject area of the X-ray detection unit 2 to be within the detection limit (counting rate limit) of the X-ray detection unit 2. A first tube current is set for the X-ray source 1 so that the X-rays detected by the non-subject area of the X-ray detector 2 are near the detection limit (near the counting rate limit). In the second X-ray imaging, the control unit 4 controls the X-ray detection unit 2 so that the X-rays detected by the subject area of the X-ray detection unit 2 do not exceed the detection limit (counting rate limit) of the X-ray detection unit 2. A second tube current is set for the X-ray source 1 so that the X-rays detected by the subject area 2 are near the detection limit (near the counting rate limit). The detection limit of the X-ray detector 2 means the upper limit of the count of X-ray photons detectable by the X-ray detector 2 per unit time (that is, the upper limit of the counting rate).

Also, the first X-ray imaging is the first X-ray imaging. Also, the second X-ray imaging is the second and subsequent X-ray imaging, and may include one or more X-ray imaging.

In the example shown in FIG. 4, X-ray imaging is performed three times in total, one first X-ray imaging and two second X-ray imaging. In addition, in the first X-ray imaging (first X-ray imaging), the area A1, which is a high counting rate area including the area outside the subject of the X-ray detection unit 2 and the edge of the subject area, X-ray imaging is performed to detect X-rays. Further, in the second X-ray imaging (second X-ray imaging), for the area A2, which is a middle counting rate area including the intermediate part between the end part and the central part of the object area of the X-ray detection unit 2, X-ray imaging is performed to detect X-rays above a reference value. In addition, in the third X-ray imaging (second X-ray imaging), X-rays equal to or greater than the reference value are detected in the area A3, which is a low counting rate area including the central portion of the subject area of the X-ray detection unit 2. An X-ray is being taken. In the graph of FIG. 4, the vertical axis indicates the count rate of X-ray photons, and the horizontal axis indicates the position (pixel) of the X-ray detection unit 2 in the X-axis direction.

Specifically, in the first X-ray imaging (first X-ray imaging), the X-ray detected by the region outside the object of the X-ray detection unit 2 with the highest counting rate is the detection limit (counting rate) of the X-ray detection unit 2. limit) is set for the X-ray source 1 (first tube current). In addition, in the first X-ray imaging (first X-ray imaging), the area A1, which is a high counting rate area including the area outside the subject of the X-ray detection unit 2 and the edge of the subject area, is subjected to X-rays of a reference value or more. A shooting time is set to detect In the first X-ray imaging (first X-ray imaging), X-rays equal to or greater than the reference value are detected in area A1, and X-rays less than the reference value are detected in areas A2 and A3.

In the second X-ray imaging (second X-ray imaging), the X-rays detected by the area A1 of the X-ray detection unit 2, which has already detected X-rays equal to or greater than the reference value, reach the detection limit (counting rate limit) of the X-ray detection unit 2. ) and the X-rays detected by the areas A2 and A3 of the X-ray detection unit 2 that have not detected X-rays equal to or greater than the reference value do not exceed the detection limit (count rate limit) of the X-ray detection unit 2. (second tube current) is set for the X-ray source 1 . Specifically, a tube current is set for the X-ray source 1 that is twice the tube current for the first X-ray imaging (first X-ray imaging). As a result, the areas A2 and A3 of the X-ray detection unit 2 can detect X-rays at a higher counting rate than in the first X-ray imaging (first X-ray imaging).

In the second X-ray imaging (second X-ray imaging), the area A2, which is the intermediate counting rate area including the intermediate part of the subject area of the X-ray detection unit 2, detects X-rays equal to or greater than the reference value during the imaging time. is set. Specifically, the area A2, which is a medium count rate area including the middle part of the subject area of the X-ray detection unit 2, detects X-rays that are equal to or greater than the reference value in the total value of the first and second X-ray imaging. time is set. In the second X-ray imaging (second X-ray imaging), X-rays equal to or greater than the reference value are detected in the area A2, and X-rays less than the reference value are detected in the area A3. Moreover, abnormal X-rays exceeding the detection limit (counting rate limit) of the X-ray detection unit 2 are detected in the area A1.

In the third X-ray imaging (second X-ray imaging), the X-rays detected by the areas A1 and A2 of the X-ray detection unit 2, which have already detected X-rays above the reference value, reach the detection limit of the X-ray detection unit 2 (count X-rays detected by the area A3 of the X-ray detection unit 2 that exceeds the X-ray detection limit (counting rate limit) of the X-ray detection unit 2 and has not detected X-rays equal to or greater than the reference value. (second tube current) is set for the X-ray source 1 . Specifically, the X-ray source 1 is set to have a tube current that is four times the tube current of the first X-ray imaging (first X-ray imaging). As a result, the region A3 of the X-ray detection unit 2 can detect X-rays at a higher counting rate than in the first and second X-ray imaging.

In addition, in the third X-ray imaging (second X-ray imaging), the area A3, which is the low counting rate area including the central part of the subject area of the X-ray detection unit 2, detects X-rays equal to or greater than the reference value during the imaging time. is set. Specifically, the area A3, which is a low count rate area including the central part of the subject area of the X-ray detection unit 2, detects X-rays that are equal to or greater than the reference value in the total value of the first to third X-ray imaging. time is set. In the third X-ray imaging (second X-ray imaging), X-rays above the reference value are detected in the region A3. Moreover, abnormal X-rays exceeding the detection limit (counting rate limit) of the X-ray detection unit 2 are detected in the areas A1 and A2. It is possible to obtain detection results of X-rays equal to or greater than the reference value in all regions (pixels) of the X-ray detection unit 2 by the first to third X-ray imaging.

In fact, in the second and third X-ray imaging, the count rate (indicated by the dashed line) of the portion exceeding the detection limit (count rate limit) of the X-ray detection unit 2 is the detection limit of the X-ray detection unit 2. Although the value is saturated at (count rate limit), in FIG. 4, the value is not saturated at the detection limit (count rate limit) of the X-ray detection unit 2. The count rate of the part exceeding is illustrated.

Further, in the first embodiment, the control unit 4 is configured to acquire image data without using the X-ray detection result of the X-ray detection unit 2 in the area outside the subject in the second X-ray imaging. Specifically, the control unit 4 does not use the detection result of the X-rays from the area outside the subject in which X-rays are detected exceeding the detection limit (counting rate limit) of the X-ray detection unit 2 in the second X-ray imaging. , configured to acquire image data. More specifically, the control unit 4 detects X-ray detection results from the object area and the outside area where X-rays are detected exceeding the detection limit (counting rate limit) of the X-ray detection unit 2 in the second X-ray imaging. is configured to acquire image data without using In the example shown in FIG. 4, the image data is obtained without using the X-ray detection result of the second X-ray imaging area A1 and the X-ray detection results of the third X-ray imaging areas A1 and A2. is obtained.

Further, in the first embodiment, the control unit 4 is configured to acquire the second X-ray imaging condition based on the X-ray detection result by the X-ray detection unit 2 in the first X-ray imaging. Specifically, the control unit 4 is configured to acquire the tube current and the imaging time in the second X-ray imaging based on the X-ray detection result by the X-ray detection unit 2 in the first X-ray imaging.

Based on the result of X-ray detection by the X-ray detection unit 2 in the first X-ray imaging, the control unit 4 detects X-rays detected by the area outside the object of the X-ray detection unit 2 in the second X-ray imaging. 2, and X-rays detected by the object region of the X-ray detection unit 2 do not exceed the detection limit (count rate limit) of the X-ray detection unit 2. is configured to Specifically, in the second X-ray imaging, the control unit 4 controls the X-rays detected by the subject region of the X-ray detection unit 2 to be within a range that does not exceed the detection limit (counting rate limit) of the X-ray detection unit 2. The X-rays detected by the subject area of the line detection unit 2 are configured to acquire the second tube current near the detection limit (near the counting rate limit). In the example shown in FIG. 4, based on the detection result of the X-ray detection unit 2 in the first X-ray imaging, the tube current in the second X-ray imaging (doubled) and the tube current in the third X-ray imaging (4 times) is obtained.

In addition, the control unit 4 determines whether the object region of the X-ray detection unit 2 detects X-rays equal to or greater than the reference value in the second X-ray imaging based on the X-ray detection result by the X-ray detection unit 2 in the first X-ray imaging. It is configured to obtain a detectable imaging time. Specifically, the control unit 4 is configured to acquire the imaging time in the second X-ray imaging based on the maximum and minimum count values of X-ray photons in the first X-ray imaging. Acquisition of the shooting time will now be described with reference to FIG. For convenience, an example in which X-ray imaging is performed twice will be described.

As shown in FIG. 5, the maximum value of X-ray photon counts is Cmax, the minimum value of X-ray photon counts is Cmin, and the ratio between the maximum value Cmax and the minimum value Cmin is R (=Cmin/Cmax ). The maximum value Cmax and the minimum value Cmin are derived from all X-ray photon detection results obtained by CT imaging in which a plurality of X-ray photon detection results are obtained while changing the X-ray irradiation position on the subject 110. It is possible. For the sake of convenience, FIG. 5 shows an example in which the detection result of a certain X-ray photon includes a maximum value Cmax and a minimum value Cmin.

Also, let S (0≦S≦1) be a value representing a boundary line (for example, a boundary line between area A1 and area A2) for obtaining a reference value in the first X-ray imaging (first X-ray imaging), and 1 Let T be the imaging time required to obtain the maximum value Cmax in one X-ray imaging. In this case, the imaging time T1 required to acquire the reference value up to the boundary value S in the first X-ray imaging (first X-ray imaging) is expressed by the following equation (1).
T1=T/(R+(1−R)×S) (1)

Also, if the reference value is N, the count value Nfirst of the pixel that is the minimum value in the first X-ray imaging (first X-ray imaging) is expressed by the following equation (2).
Nfirst=N×R/(R+(1−R)×S) (2)

Also, the count value Nsecond required to obtain the reference value N at the pixel with the minimum value in the second X-ray imaging (second X-ray imaging) is expressed by the following equation (3).
Nsecond=N−Nfirst=N×(1−R/(R+(1−R)×S)) (3)

Also, the imaging time T2 required for counting the count value Nsecond in the second X-ray imaging (second X-ray imaging) is expressed by the following equation (4).
T2=T×(1−R/(R+(1−R)×S))×(R+(1−R)×S) (4)

In this way, the imaging time of the second X-ray imaging (second X-ray imaging) can be represented by a relational expression in which the ratio R and the boundary value S are variables, and can be obtained. In addition, although the relational expression becomes more complicated than when X-ray imaging is performed twice, even when performing X-ray imaging three times or more, the imaging time of the second X-ray imaging is the ratio R and It is possible to express and acquire the boundary value S by a relational expression in which the variable is a variable.

Note that the total value Ttotal of the imaging times when X-ray imaging is performed twice is expressed by the following equation (5).
Ttotal=T1+T2=T/(R+(1-R)×S)+T×(1-R/(R+(1-R)×S))×(R+(1-R)×S) ・・・( 5)

Also, the imaging time Tonce when X-ray imaging is performed only once corresponds to S=0, and is represented by the following equation (6).
Tone=T/R (6)

FIG. 6 shows an example of a graph of the reduction rate of imaging time when X-ray imaging is performed 1 to 4 times. In the graph of FIG. 6, the vertical axis indicates the reduction rate of imaging time when X-ray imaging is performed only once, and the horizontal axis indicates the ratio R between the maximum value Cmax and the minimum value Cmin. As shown in the graph of FIG. 6, the smaller the value of the ratio R, the greater the shortening rate of the imaging time compared to the case where only one X-ray imaging is performed. Also, the greater the number of times of imaging, the greater the reduction rate of the imaging time in the case of performing X-ray imaging only once. In addition, when the value of the ratio R is small, the radiographing time is greatly shortened when X-ray imaging is performed two to four times, compared to when X-ray imaging is performed only once. Moreover, the reduction rate of the imaging time does not increase so much between the case of performing X-ray imaging three times and the case of performing X-ray imaging four times. In addition, since the complexity caused by the increase in the number of times of photographing also increases, it is desirable to determine the number of times of photographing in consideration of both the effect of shortening the photographing time and the complexity caused by the increase in the number of times of photographing.

FIG. 7 shows a graph combining X-ray photon detection results obtained by the first X-ray imaging and the second X-ray imaging. In the graph of FIG. 7, the vertical axis indicates the number of X-ray photons counted, and the horizontal axis indicates the position (pixel) of the X-ray detection unit 2 in the X-axis direction. As shown in FIG. 7, in all the regions (A1 to A3) of the X-ray detector 2, X-rays equal to or greater than the reference value (reference count number) are detected. On the other hand, the state of the graph in FIG. 7 is not data suitable for obtaining image data (reconstructed image data), so it is necessary to convert the data into data suitable for obtaining image data (reconstructed image data). Note that the graph of FIG. 7 does not include detection results of abnormal X-rays obtained beyond the detection limit of the X-ray detection unit 2 .

Therefore, in the first embodiment, as shown in FIGS. 7 and 8, the control unit 4 controls the first X-ray imaging and the second X-ray imaging based on the tube current and the imaging time of the first X-ray imaging and the second X-ray imaging. It is configured to reconstruct the X-ray detection result by the X-ray detection unit 2 in imaging. Specifically, the control unit 4 converts the X-ray detection result by the X-ray detection unit 2 in the other X-ray imaging based on the tube current and imaging time of the last X-ray imaging of the second X-ray imaging. Thus, the X-ray detection results of the X-ray detector 2 in the first X-ray imaging and the second X-ray imaging are reconstructed.

For example, the tube current for the first X-ray imaging (first X-ray imaging) is 1 and the imaging time is 1 second, and the tube current for the second X-ray imaging (second X-ray imaging) is 2. Assume that the imaging time is 1 second, the tube current for the third X-ray imaging (second X-ray imaging) is 4 times, and the imaging time is 1 second. In this case, the X-ray detection result of the first X-ray imaging (first X-ray imaging) is the product (1×1) of the tube current and the imaging time of the first X-ray imaging (first X-ray imaging). The ratio (4×1/(1×1)) of the product (4×1) of the tube current and the imaging time of the third X-ray imaging (second X-ray imaging) is converted to be four times . Similarly, the X-ray detection result of the second X-ray imaging (second X-ray imaging) is the product (2×1) of the tube current and the imaging time of the second X-ray imaging (second X-ray imaging). Converted to be doubled by the ratio (4×1/(2×1)) of the product (4×1) of the tube current and the imaging time of the third X-ray imaging (second X-ray imaging) . That is, the X-ray detection results of the first X-ray imaging and the second X-ray imaging are converted by converting the X-ray detection results of other X-ray imaging based on the X-ray detection results of the last X-ray imaging. is reconstructed. Then, image data (reconstructed image data) is acquired based on the reconstructed X-ray detection result.

(simulation result)
Next, with reference to FIGS. 9 and 10, simulation results for confirming the image quality of reconstructed images obtained by the first X-ray imaging and the second X-ray imaging will be described.

In the simulation, a cylindrical resin member in which high-density resin was embedded at five locations was used as a subject. In addition, for this object, a reconstructed image (comparative example) was obtained by X-ray imaging only once, and a reconstructed image (example) was obtained by X-ray imaging three times.

As shown in FIG. 9, the X-ray detection result before reconstruction obtained by combining the X-ray photon detection results obtained by three times of X-ray imaging has the same shape as the graph shown in FIG. However, by reconstruction, the shape is restored to the same shape as the X-ray photon detection result obtained by only one X-ray imaging. In addition, in the detection result of X-rays after reconstruction obtained by X-ray imaging three times, the area outside the subject (high count region) has a large variation in the number of counts. However, since X-rays exceeding the reference value are detected in the area outside the object (high count area), there is no problem in image quality.

As shown in FIG. 10, the reconstructed image acquired by one X-ray imaging and the reconstructed image acquired by three X-ray imaging were compared in regions B1 and B2. A region B1 is a region that includes only the base material of the resin member that is the subject. A region B2 is a region containing only the high-density resin of the resin member, which is the subject. The average value and standard deviation of pixel values were obtained in regions B1 and B2. It was equivalent to the reconstructed image acquired by That is, the reconstructed image obtained by three times of X-ray imaging had the same image quality as the reconstructed image obtained by only one time of X-ray imaging. Further, as described above, in the detection results of X-rays after reconstruction obtained by three times of X-ray imaging, compared with the detection results of X-ray photons obtained by only one time of X-ray imaging, the subject Although the variation in the number of counts in the outer region (high count region) was large, this variation (noise) did not affect the image quality of the subject.

(X-ray imaging processing)
Next, referring to FIG. 11, X-ray imaging processing by the X-ray imaging apparatus 100 of the first embodiment will be described based on a flowchart. Each process in the flowchart is performed by the control unit 4 . Also, for the sake of convenience, an example in which X-ray imaging is performed three times will be described.

As shown in FIG. 11, first, in step 101, preprocessing X-ray imaging is performed with no subject 110 installed. In step 101, based on preprocessing X-ray imaging without the subject 110 installed, blank data obtained by imaging only the outside of the subject 110 without the subject 110 being captured is acquired.

Then, in step 102, conditions for the first X-ray imaging (first X-ray imaging conditions) are determined. For example, in step 102, a predetermined tube current and imaging time are determined as first X-ray imaging conditions. Further, for example, in step 102, based on the blank data obtained in step 101, the tube current and the imaging time are obtained and determined as the first X-ray imaging conditions. In this case, for example, based on the X-ray photon count rate for each pixel of the blank data obtained in step 101 , the tube current is obtained so that the X-ray photon count rate is suitable for the outside of the subject 110 . Also, the imaging time corresponding to this tube current is obtained. This makes it possible to determine the tube current and the imaging time in consideration of aging deterioration of the X-ray source 1 and the X-ray detector 2 .

Also, between step 102 and step 103 , subject 110 is placed on rotating stage 3 .

Then, in step 103, the first X-ray imaging (first X-ray imaging) is performed under the first X-ray imaging conditions determined in step 102. FIG. In step 103, CT imaging is performed to obtain a plurality of X-ray detection results while changing the irradiation position (rotation angle position) of X-rays with respect to the object 110 under the first X-ray imaging conditions determined in step 102. FIG. As a result, the X-ray detection result of the first X-ray imaging for each X-ray irradiation position (rotation angle position) on the object 110 is acquired.

Then, in step 104, the conditions for the second and third X-ray imaging (second X-ray imaging conditions) are determined. In step 104, based on the X-ray detection result of the first X-ray imaging (first X-ray imaging) performed in Step 103, the second and third tube currents and imaging times are determined.

Then, in step 105, the second X-ray imaging (second X-ray imaging) is performed under the second X-ray imaging conditions determined in step 104. FIG. In step 105, CT imaging is performed to obtain a plurality of X-ray detection results while changing the X-ray irradiation position (rotation angle position) with respect to the object 110 under the second X-ray imaging conditions determined in step 104. FIG. As a result, the X-ray detection result of the second X-ray imaging (second X-ray imaging) for each X-ray irradiation position (rotation angle position) of the object 110 is acquired.

Then, in step 106, the third X-ray imaging (second X-ray imaging) is performed under the second X-ray imaging conditions determined in step 104. FIG. In step 106, CT imaging is performed to obtain a plurality of X-ray detection results while changing the X-ray irradiation position (rotation angle position) with respect to the subject 110 under the second X-ray imaging conditions determined in step 104. FIG. As a result, the X-ray detection result of the third X-ray imaging (second X-ray imaging) for each X-ray irradiation position (rotation angle position) of the object 110 is obtained.

Then, in step 107, the data of the X-ray detection results of the first to third X-ray imaging are combined. In step 107 , the data of the X-ray detection results of the first to third X-ray imaging are combined for each X-ray irradiation position (rotation angle position) with respect to the subject 110 .

Then, in step 108, the data of the X-ray detection results of the first to third X-ray imaging combined in step 107 are reconstructed. In step 108, the data of the X-ray detection results of the first to third X-ray imaging combined in step 107 is reconstructed for each X-ray irradiation position (rotation angle position) on the subject 110. FIG.

Then, in step 109 , a reconstructed image is generated based on the data reconstructed in step 108 .

(Effect of the first embodiment)
The following effects can be obtained in the first embodiment.

In the first embodiment, as described above, the X-ray imaging apparatus 100 includes the X-ray source 1, the X-ray detection unit 2 that detects X-rays emitted from the X-ray source 1, the X-ray source 1 and the X-ray and a control unit 4 for controlling conditions for X-ray imaging of the subject 110 by the line detection unit 2 . In the first X-ray imaging, the control unit 4 sets the first X-ray imaging conditions under which the region outside the object of the X-ray detection unit 2 can detect X-rays of a reference value or more required for imaging, and performs the first X-ray imaging. In the second X-ray imaging performed later, the object area of the X-ray detection unit 2 is configured to set a second X-ray imaging condition under which X-rays of a reference value or more can be detected. Further, the X-ray imaging method includes the step of detecting X-rays by the X-ray detection unit 2; a step of performing a first X-ray imaging under radiographic conditions; and a step of performing a second X-ray imaging after the first X-ray imaging under a second X-ray imaging conditions in which the object region of the X-ray detection unit 2 can detect X-rays equal to or greater than a reference value. and a step of photographing.

As a result, detection of X-rays in the object area by the second X-ray imaging can be performed independently of detection of X-rays in the area outside the object by the first X-ray imaging. It is possible to set imaging conditions that do not consider the detection of X-rays in the area. As a result, the second X-ray imaging condition can be set to an imaging condition that increases the X-ray dose detected per unit time in the subject area without considering detection of X-rays in the area outside the subject. can be shortened. In addition, X-ray detection in the non-object area by the first X-ray imaging can be performed independently of detection of X-rays in the non-object area by the second X-ray imaging. It is possible to suppress the detection of X-rays that far exceed the reference value required for the conversion. Further, as described above, the first X-ray imaging is performed under the first X-ray imaging conditions under which the area outside the object of the X-ray detection unit 2 can detect X-rays equal to or greater than the reference value necessary for imaging, and the X-ray imaging is performed. Since the second X-ray imaging is performed under the second X-ray imaging conditions in which the subject area of the detection unit 2 can detect X-rays equal to or greater than the reference value, the area outside the subject and the subject area are detected by the first X-ray imaging and the second X-ray imaging. Both can detect X-rays above the threshold required for imaging. As a result, it is possible to shorten the imaging time while detecting X-rays above the reference value required for imaging in both the non-subject area and the subject area. Although the "object area" varies depending on the size of the object 110, normally if it is set at the edge of the X-ray detection unit 2, the effect can be obtained, and the "object area" is the inside of the object area. As for the region, if it is usually set in the center of the X-ray detection unit 2, the effect can be obtained.

Further, in the above-described embodiment, the following further effects can be obtained by configuring as follows.

That is, in the first embodiment, as described above, the control unit 4 is configured to change the X-ray imaging conditions by controlling the tube current of the X-ray source 1 . The step of performing the second X-ray imaging includes at least one of the tube current of the X-ray source 1 and the positional relationship among the X-ray source 1, the object 110, and the X-ray detection unit 2 in the optical axis direction of X-rays. and changing the conditions of X-ray imaging by controlling . By controlling the tube current of the X-ray source 1, which is related to the amount of detected X-rays, and changing the conditions of X-ray imaging, X-rays are detected per unit time in the subject area by the second X-ray imaging. X-ray dose can be increased.

Further, in the first embodiment, as described above, the control unit 4 sets the first tube current to the X-ray source 1 in the first X-ray imaging, and sets the first tube current to the X-ray source 1 in the second X-ray imaging. is configured to set a second tube current that is also large for the X-ray source 1 . Also, the step of performing the first X-ray imaging includes the step of performing the first X-ray imaging with the X-ray source 1 in which the first tube current is set. Also, the step of performing the second X-ray imaging includes the step of performing the second X-ray imaging with the X-ray source 1 in which the second tube current is set higher than the first tube current. As a result, the X-ray dose detected per unit time in the object region by the second X-ray imaging can be easily increased simply by changing the tube current of the X-ray source 1 from the first tube current to the second tube current. Therefore, the shooting time can be easily shortened.

Further, in the first embodiment, as described above, the control unit 4 prevents the X-rays detected by the extra-object region of the X-ray detection unit 2 from exceeding the detection limit of the X-ray detection unit 2 in the first X-ray imaging. The first tube current is set for the X-ray source 1, and in the second X-ray imaging, the X-rays detected by the extra-object region of the X-ray detection unit 2 exceed the detection limit of the X-ray detection unit 2, and the X-ray A second tube current is set for the X-ray source 1 so that the X-rays detected by the subject area of the line detection unit 2 do not exceed the detection limit of the X-ray detection unit 2 . In the step of performing the first X-ray imaging, the X-ray source 1 is set to a first tube current that does not exceed the detection limit of the X-ray detection unit 2 for the X-rays detected by the region outside the object of the X-ray detection unit 2, The step of taking a first radiograph is included. In the step of performing the second X-ray imaging, the X-rays detected by the non-subject area of the X-ray detection unit 2 exceed the detection limit of the X-ray detection unit 2 and the X-rays detected by the subject area of the X-ray detection unit 2 are detected. is set to a second tube current that does not exceed the detection limit of the X-ray detector 2, and performs a second X-ray imaging. As a result, the first X-ray imaging can be performed with the X-ray source 1 setting the first tube current such that the X-rays detected by the X-ray detection unit 2 outside the subject area do not exceed the detection limit of the X-ray detection unit 2. Therefore, unlike the case where the X-ray source 1 sets the tube current exceeding the detection limit of the X-ray detection unit 2, the X-rays detected by the extra-subject area of the X-ray detection unit 2 are different from the first X-ray imaging. A normal detection result can be obtained in the area outside the object by one X-ray imaging. Further, the second X-ray imaging can be performed with the X-ray source 1 setting the second tube current such that the X-rays detected by the object region of the X-ray detection unit 2 do not exceed the detection limit of the X-ray detection unit 2. , X-rays detected by the object region of the X-ray detection unit 2 are set to a second tube current that exceeds the detection limit of the X-ray detection unit 2. Unlike the case of performing the second X-ray imaging, the second X-ray A normal detection result can be obtained in the area outside the subject by line photography. Further, the second X-ray imaging can be performed with the X-ray source 1 setting the second tube current exceeding the detection limit of the X-ray detection unit 2 for the X-rays detected by the region outside the object of the X-ray detection unit 2. , X-rays detected by the area outside the object of the X-ray detection unit 2 are set to a tube current that does not exceed the detection limit of the X-ray detection unit 2, and the second X-ray imaging is performed. 2 X-ray imaging can increase the amount of X-rays detected per unit time in the object region.

Further, in the first embodiment, as described above, image data is acquired without using the X-ray detection result of the X-ray detection unit 2 in the area outside the subject in the second X-ray imaging. As a result, image data can be acquired without using the detection result of abnormal X-rays from the region outside the object of the X-ray detection unit 2 in the second X-ray imaging, so that the image data can be acquired accurately. .

Further, in the first embodiment, as described above, X-ray detection by the X-ray detector 2 in the first X-ray imaging and the second X-ray imaging is performed based on the tube current and the imaging time of the first X-ray imaging and the second X-ray imaging. is configured to reconstruct the detection results of As a result, even when the first X-ray imaging and the second X-ray imaging are performed separately, the X-ray detection result by the X-ray detection unit 2 in the first X-ray imaging and the X-ray detection result by the X-ray detection unit 2 in the second X-ray imaging are detected. The line detection results can be converted into data suitable for obtaining image data. As a result, image data can be easily acquired even when the first X-ray imaging and the second X-ray imaging are performed separately.

Further, in the first embodiment, as described above, based on the tube current and the imaging time of the last X-ray imaging of the second X-ray imaging, the X-ray detection result by the X-ray detection unit 2 in another X-ray imaging By converting , the X-ray detection result by the X-ray detection unit 2 in the first X-ray imaging and the second X-ray imaging is reconstructed. As a result, the X-ray detection result by the X-ray detection unit 2 in the first X-ray imaging and the X-ray detection result by the X-ray detection unit 2 in the second X-ray imaging can be easily converted into data suitable for obtaining image data. and can be reliably converted.

Further, in the first embodiment, as described above, the control unit 4 is configured to acquire the second X-ray imaging condition based on the X-ray detection result by the X-ray detection unit 2 in the first X-ray imaging. ing. As a result, the second X-ray imaging conditions can be acquired in consideration of the X-ray detection result by the X-ray detection unit 2 in the first X-ray imaging. In comparison, more appropriate second X-ray imaging conditions can be obtained.

In addition, in the first embodiment, as described above, the X-ray detector 2 is configured to detect X-ray photons. In addition, the control unit 4 sets a first X-ray imaging condition under which the region outside the object of the X-ray detection unit 2 detects X-ray photons equal to or greater than the reference count number required for imaging in the first X-ray imaging, and In the second X-ray imaging, the subject area of the X-ray detection unit 2 is configured to set a second X-ray imaging condition for detecting X-ray photons equal to or greater than the reference count number. Further, the step of detecting X-rays by the X-ray detection unit 2 includes the step of detecting X-ray photons by the X-ray detection unit 2 . In the step of performing the first X-ray imaging, the first X-ray imaging is performed under the first X-ray imaging conditions under which the area outside the object of the X-ray detection unit 2 can detect X-ray photons equal to or greater than the reference count number required for imaging. including the step of The step of performing the second X-ray imaging includes the step of performing the second X-ray imaging under a second X-ray imaging condition in which the subject area of the X-ray detection unit 2 can detect X-ray photons equal to or greater than the reference count. As a result, in the configuration in which the X-ray detection unit 2 detects X-ray photons, it is possible to shorten the imaging time while detecting X-rays of a reference value or more necessary for imaging in both the area outside the subject and the subject area. can.

[Second embodiment]
Next, a second embodiment of the present invention will be described with reference to FIGS. 12 and 13. FIG. In the second embodiment, unlike the first embodiment in which the tube current of the X-ray source is controlled, an example will be described in which the positional relationship between the X-ray source, the object and the X-ray detector is controlled. In the drawings, the same components as in the first embodiment are indicated by the same reference numerals, and descriptions thereof are omitted.

(Configuration of X-ray imaging device)
As shown in FIG. 12, an X-ray imaging apparatus 200 includes a rotating stage 203 and a control section 204 instead of the rotating stage 3 and control section 4 of the first embodiment.

Rotation stage 203 is configured to rotate object 110 . The rotating stage 203 includes a mounting table for mounting the subject 110 and a drive unit such as a motor for rotating the mounting table. In addition, the rotating stage 203 further includes a driving unit such as a motor that drives the mounting table to advance in the optical axis direction of X-rays. Rotating stage 203 is configured to rotate under the control of control unit 204 . By rotating the subject 110 with the rotation stage 203 , the subject 110 can be rotated with respect to the imaging system including the X-ray source 1 and the X-ray detector 2 . As a result, X-ray imaging can be performed while changing the X-ray irradiation position on the object 110 . Further, the rotating stage 203 is configured to be linearly moved in the direction of the optical axis of X-rays under the control of the control unit 204 . As a result, X-ray imaging can be performed while changing the positional relationship among the X-ray source 1, the object 110, and the X-ray detector 2 in the X-ray optical axis direction.

The control unit 204 is configured to control each unit of the X-ray imaging apparatus 200 . The control unit 204 includes a processor such as a CPU (Central Processing Unit) and a memory. Further, the control unit 204 functions as an image processing unit that performs data processing regarding images. Specifically, the control unit 204 is configured to acquire a plurality of sinogram image data corresponding to a plurality of energy ranges (a plurality of bins) based on the detection result of X-ray photons by the X-ray detection unit 2. ing. The sinogram image data is image data obtained by two-dimensionally arranging the detection results of X-ray photons by the X-ray detection unit 2 according to the number of the detection element (detector number) and the rotation angle.

The control unit 204 is configured to acquire reconstructed image data by performing reconstruction processing such as FBP (Filtered Back Projection) on sinogram image data. Note that reconstructed image data can be obtained for each sinogram image data. That is, it is possible to obtain a plurality of reconstructed image data based on a plurality of sinogram image data. Further, the control unit 204 is configured to perform material discrimination of the subject 110 based on a plurality of pieces of reconstructed image data.

Here, in the second embodiment, as shown in FIG. 13, the control unit 204 is configured to control the conditions for X-ray imaging of the subject 110 by the X-ray source 1 and the X-ray detection unit 2. . Specifically, in the first X-ray imaging, the control unit 204 sets the first X-ray imaging conditions under which the region outside the object of the X-ray detection unit 2 can detect X-rays of a reference value or more necessary for imaging. In the second X-ray imaging performed after the first X-ray imaging, the object region of the X-ray detector 2 is configured to set a second X-ray imaging condition under which X-rays equal to or greater than the reference value can be detected. That is, the X-ray imaging apparatus 200 performs the first X-ray imaging under the first X-ray imaging conditions in which the X-ray detection unit 2 can detect X-rays of a reference value or more in the area outside the subject, and the X-ray detection unit 2 The subject area is configured to perform the second X-ray imaging after the first X-ray imaging under the second X-ray imaging conditions under which X-rays equal to or greater than the reference value can be detected.

More specifically, in the first X-ray imaging, the control unit 204 sets the first X-ray imaging conditions under which the area outside the subject of the X-ray detection unit 2 can detect X-ray photons equal to or greater than the reference count required for imaging. is set, and in the second X-ray imaging, the object region of the X-ray detection unit 2 is configured to set a second X-ray imaging condition under which X-ray photons equal to or larger than the reference count can be detected. That is, the X-ray imaging apparatus 200 performs the first X-ray imaging under the first X-ray imaging conditions under which the X-ray detection unit 2 can detect X-ray photons equal to or greater than the reference count number, and the X-ray detection unit 2 subject regions are configured to perform second X-ray imaging under second X-ray imaging conditions under which X-ray photons equal to or greater than the reference count can be detected. Note that the reference count number is the minimum count number required to obtain a reconstructed image with sufficient image quality. The reference count number is obtained in advance through experiments or the like.

In the second embodiment, the control unit 204 changes the X-ray imaging conditions by controlling the positional relationship between the X-ray source 1, the subject 110, and the X-ray detection unit 2 in the X-ray optical axis direction. is configured to Specifically, the control unit 4 sets the positional relationship among the X-ray source 1, the subject 110, and the X-ray detection unit 2 to the initial positions in the first X-ray imaging, and in the second X-ray imaging, X-ray The positional relationship between the radiation source 1, the subject 110, and the X-ray detection unit 2 is set to a second X-ray imaging position where the subject 110 can be imaged at a higher magnification than the first X-ray imaging. there is Note that in the second embodiment, the tube current is not changed between the first X-ray imaging and the second X-ray imaging.

In the example shown in FIG. 13, X-ray imaging is performed three times in total, one first X-ray imaging and two second X-ray imaging. In addition, in the first X-ray imaging (first X-ray imaging), the area A1, which is a high counting rate area including the area outside the subject of the X-ray detection unit 2 and the edge of the subject area, X-ray imaging is performed to detect X-rays. Further, in the second X-ray imaging (second X-ray imaging), for the area A2, which is a middle counting rate area including the intermediate part between the end part and the central part of the object area of the X-ray detection unit 2, X-ray imaging is performed to detect X-rays above a reference value. In addition, in the third X-ray imaging (second X-ray imaging), X-rays equal to or greater than the reference value are detected in the area A3, which is a low counting rate area including the central portion of the subject area of the X-ray detection unit 2. An X-ray is being taken. In the graph of FIG. 13, the vertical axis indicates the count rate of X-ray photons, and the horizontal axis indicates the position (pixel) of the X-ray detection unit 2 in the X-axis direction.

Specifically, in the first X-ray imaging (first X-ray imaging), the positional relationship among the X-ray source 1, subject 110, and X-ray detector 2 is set to the initial position. In addition, in the first X-ray imaging (first X-ray imaging), in the area A1, which is a high counting rate area including the area outside the subject of the X-ray detection unit 2 and the edge of the subject area, X-rays of a reference value or more is detected. In the first X-ray imaging (first X-ray imaging), X-rays equal to or greater than the reference value are detected in area A1, and X-rays less than the reference value are detected in areas A2 and A3.

In the second X-ray imaging (second X-ray imaging), the positional relationship between the X-ray source 1, the subject 110, and the X-ray detection unit 2 is such that the area A1 is out of the imaging range, and the first X-ray imaging ( The second X-ray imaging position is set so that the object 110 can be imaged at a higher magnification than the first X-ray imaging. Specifically, by moving the rotating stage 203 in the X-ray optical axis direction, the subject 110 is moved to a position closer to the X-ray source 1 than in the first X-ray imaging (first X-ray imaging). there is As a result, the areas A2 and A3 of the X-ray detection unit 2 can detect X-rays at a higher magnification (wider range) than in the first X-ray imaging (first X-ray imaging). As a result, in the areas A2 and A3 of the X-ray detection unit 2, it is possible to increase the amount of detected X-rays per unit time compared to the first X-ray imaging (first X-ray imaging).

In addition, in the second X-ray imaging (second X-ray imaging), X-rays equal to or greater than the reference value are detected in the area A2, which is the middle counting rate area including the middle part of the subject area of the X-ray detection unit 2. . Specifically, in the region A2, which is a medium count rate region including the middle portion of the subject region of the X-ray detection unit 2, X-rays that are equal to or greater than the reference value in the total value of the first and second X-ray imaging are detected. there is In the second X-ray imaging (second X-ray imaging), X-rays equal to or greater than the reference value are detected in the area A2, and X-rays less than the reference value are detected in the area A3. Further, since the area A1 is outside the imaging range, no X-rays are detected.

In the third X-ray imaging (second X-ray imaging), the positional relationship between the X-ray source 1, the subject 110, and the X-ray detection unit 2 is such that the areas A1 and A2 are out of the imaging range, and the second X-ray imaging is performed. The second X-ray imaging position is set so that the subject 110 can be imaged at a higher magnification than the imaging (second X-ray imaging). Specifically, by moving the rotating stage 203 in the X-ray optical axis direction, the subject 110 is moved to a position closer to the X-ray source 1 than in the second X-ray imaging (second X-ray imaging). there is As a result, the area A3 of the X-ray detection unit 2 can detect X-rays at a higher magnification (wider range) than in the first and second X-ray imaging (first X-ray imaging). As a result, in the region A3 of the X-ray detection unit 2, it is possible to increase the amount of detected X-rays per unit time compared to the first and second X-ray imaging.

In addition, in the third X-ray imaging (second X-ray imaging), X-rays equal to or greater than the reference value are detected in the area A3, which is the low counting rate area including the central portion of the subject area of the X-ray detection unit 2. . Specifically, in the region A3, which is a low count rate region including the central portion of the subject region of the X-ray detection unit 2, X-rays that are equal to or greater than the reference value in the total value of the first to third X-ray imaging are detected. there is In the third X-ray imaging (second X-ray imaging), X-rays above the reference value are detected in the region A3. Further, since the regions A1 and A2 are outside the imaging range, X-ray detection is not performed.

In the second embodiment, the control unit 204 performs processing to reduce the difference in magnification of the subject 110 based on the magnification of the subject 110 in the first X-ray imaging and the second X-ray imaging. It is configured to reconstruct the X-ray detection result by the X-ray detection unit 2 in the second X-ray imaging.

Other configurations of the second embodiment are the same as those of the first embodiment.

(Effect of Second Embodiment)
The following effects can be obtained in the second embodiment.

In the second embodiment, as described above, the X-ray imaging apparatus 200 includes the X-ray source 1, the X-ray detector 2 that detects X-rays emitted from the X-ray source 1, the X-ray source 1 and the X-ray and a control unit 204 that controls conditions for X-ray imaging of the subject 110 by the line detection unit 2 . In the first X-ray imaging, the control unit 204 sets a first X-ray imaging condition under which the area outside the subject of the X-ray detection unit 2 can detect X-rays of a reference value or more necessary for imaging, and performs the first X-ray imaging. In the second X-ray imaging performed later, the object area of the X-ray detection unit 2 is configured to set a second X-ray imaging condition under which X-rays of a reference value or more can be detected. Further, the X-ray imaging method includes the step of detecting X-rays by the X-ray detection unit 2; a step of performing a first X-ray imaging under radiographic conditions; and a step of performing a second X-ray imaging after the first X-ray imaging under a second X-ray imaging conditions in which the object region of the X-ray detection unit 2 can detect X-rays equal to or greater than a reference value. and a step of photographing.

As a result, as in the first embodiment, it is possible to shorten the imaging time while detecting X-rays of a reference value or more required for imaging in both the non-subject area and the subject area.

Further, in the second embodiment, as described above, the control unit 204 controls the positional relationship between the X-ray source 1, the subject 110, and the X-ray detection unit 2 in the X-ray optical axis direction to It is configured to change the shooting conditions. The step of performing the second X-ray imaging is a step of changing the conditions of X-ray imaging by controlling the positional relationship between the X-ray source 1, the subject 110, and the X-ray detector 2 in the X-ray optical axis direction. including. Thus, by controlling the positional relationship between the X-ray source, the subject, and the X-ray detector in the direction of the X-ray optical axis, which is related to the detected amount of X-rays, the X-ray imaging conditions can be changed. 2 X-ray imaging can increase the amount of X-rays detected per unit time in the object region.

Other effects of the second embodiment are the same as those of the first embodiment.

[Modification]
It should be noted that the embodiments disclosed this time should be considered as examples and not restrictive in all respects. The scope of the present invention is indicated by the scope of the claims rather than the description of the above-described embodiments, and includes all modifications (modifications) within the meaning and scope equivalent to the scope of the claims.

For example, in the above-described first and second embodiments, an example in which the present invention is applied to an X-ray imaging apparatus as a CT apparatus including a photon-counting X-ray detection unit has been described, but the present invention is limited to this. do not have. The present invention may be applied to an X-ray imaging apparatus as a normal CT apparatus having an integral X-ray detection unit that is not a photon counting type. A normal CT apparatus having an integral X-ray detection unit also has the same problem as a CT apparatus having a photon counting X-ray detection unit.

FIG. 14 shows a graph of the distribution of X-ray energy readout values per unit time in the integration type X-ray detector when a cylindrical subject is imaged. In the graph of FIG. 14 , the vertical axis indicates the energy readout value of X-rays per unit time, and the horizontal axis indicates the position (pixel) in the X-axis direction of the integral type X-ray detection unit. In the graph of FIG. 14, the X-ray energy reading value per unit time is large at both ends in the X-axis direction corresponding to the non-object area, and the X-ray unit The energy readout per hour is getting smaller.

In addition, the integral type X-ray detector has an upper limit value of the energy reading value of X-rays that can be detected per unit time. When the integral type X-ray detector detects X-rays exceeding the upper limit value, it reads an energy value smaller than the actual energy value, so that a normal X-ray energy value cannot be obtained. For this reason, even in a normal CT apparatus equipped with an integral type X-ray detection unit, it is possible to shorten the imaging time while detecting X-rays above the reference value necessary for imaging in both the area outside the object and the object area. is desired.

Further, in the above-described first and second embodiments, an example in which the subject is rotated with respect to the imaging system including the X-ray source and the X-ray detection unit has been described, but the present invention is not limited to this. In the present invention, X-ray imaging may be performed while changing the X-ray irradiation position on the subject by rotating the imaging system including the X-ray source and the X-ray detector with respect to the subject.

Also, in the above-described first and second embodiments, an example in which the control section functions as an image processing section has been described, but the present invention is not limited to this. In the present invention, an image processing section including a processor such as a GPU (Graphics Processing Unit) may be provided separately from the control section. In this case, the image processing unit may perform image-related processing such as reconstruction of X-ray detection results and acquisition of image data.

Also, in the above-described first and second embodiments, an example in which the second X-ray imaging is performed twice has been shown, but the present invention is not limited to this. In the present invention, the second X-ray imaging may be performed once, or three or more times.

Further, in the first and second embodiments, in the first X-ray imaging, the high count rate region including the non-subject region of the X-ray detection unit and the edge of the subject region is subjected to the reference value or more. Although an example of X-ray imaging that detects X-rays has been shown, the present invention is not limited to this. In the present invention, in the first X-ray imaging, X-ray imaging for detecting X-rays equal to or higher than the reference value may be performed on a high counting rate area including only the non-subject area of the X-ray detection unit.

Further, in the second embodiment, an example is shown in which the positional relationship between the X-ray source, the subject, and the X-ray detector in the X-ray optical axis direction is changed by moving the subject in the X-ray optical axis direction. However, the present invention is not limited to this. In the present invention, by moving at least one of the X-ray source, the object, and the X-ray detector in the X-ray optical axis direction, the X-ray source, the object, and the X-ray detector move in the X-ray optical axis direction. You may change the positional relationship.

In the first embodiment, an example of controlling the tube current of the X-ray source is shown. Although an example of controlling is shown, the present invention is not limited to this. In the present invention, X-ray imaging conditions are changed by controlling both the tube current of the X-ray source and the positional relationship between the X-ray source, the object and the X-ray detector in the direction of the X-ray optical axis. may

[Aspect]
It will be appreciated by those skilled in the art that the exemplary embodiments described above are specific examples of the following aspects.

(Item 1)
an x-ray source;
an X-ray detector that detects X-rays emitted from the X-ray source;
a control unit that controls conditions for X-ray imaging of a subject by the X-ray source and the X-ray detection unit;
In the first X-ray imaging, the control unit sets a first X-ray imaging condition under which the region outside the object of the X-ray detection unit can detect the X-rays having a reference value or more required for imaging, and the first X-ray imaging In a second X-ray imaging performed after radiography, the subject area of the X-ray detection unit is configured to set a second X-ray imaging condition that allows detection of the X-rays equal to or greater than the reference value. photographic equipment.

(Item 2)
The control unit controls at least one of a tube current of the X-ray source and a positional relationship among the X-ray source, the subject, and the X-ray detection unit in the optical axis direction of the X-rays. , the X-ray imaging apparatus according to item 1, configured to change the conditions of X-ray imaging.

(Item 3)
The control unit sets a first tube current to the X-ray source in the first X-ray imaging, and sets a second tube current larger than the first tube current in the second X-ray imaging. 3. Radiographic apparatus according to item 2, configured to be set to a source.

(Item 4)
In the first X-ray imaging, the control unit controls the X-ray source so that the X-rays detected by the extra-subject area of the X-ray detection unit do not exceed the detection limit of the X-ray detection unit. and in the second X-ray imaging, the X-ray detected by the extra-object area of the X-ray detection unit exceeds the detection limit of the X-ray detection unit, and the X-ray detection unit X-ray imaging according to item 3, wherein the second tube current is set for the X-ray source such that the X-rays detected by the object region do not exceed the detection limit of the X-ray detection unit. Device.

(Item 5)
5. The X-ray imaging apparatus according to item 4, configured to acquire image data without using the detection result of the X-rays from the extra-object area of the X-ray detection unit in the second X-ray imaging.

(Item 6)
reconstructing the detection result of the X-rays by the X-ray detection unit in the first X-ray imaging and the second X-ray imaging based on the tube current and the imaging time of the first X-ray imaging and the second X-ray imaging 6. The X-ray imaging apparatus according to any one of items 2 to 5, wherein

(Item 7)
By converting the detection result of the X-rays by the X-ray detection unit in another X-ray imaging based on the tube current and the imaging time of the last X-ray imaging of the second X-ray imaging, the first X-ray imaging and the X-ray imaging apparatus according to Item 6, configured to reconstruct the detection result of the X-rays by the X-ray detection unit in the second X-ray imaging.

(Item 8)
any one of items 1 to 7, wherein the control unit is configured to acquire the second X-ray imaging condition based on a detection result of the X-rays by the X-ray detection unit in the first X-ray imaging The X-ray imaging apparatus according to item 1.

(Item 9)
The X-ray detection unit is configured to detect X-ray photons,
The control unit sets the first X-ray imaging conditions under which the extra-subject area of the X-ray detection unit can detect the X-ray photons equal to or greater than a reference count required for imaging in the first X-ray imaging. and in the second X-ray imaging, the subject region of the X-ray detection unit is configured to set the second X-ray imaging conditions under which the X-ray photons equal to or greater than the reference count can be detected. The X-ray imaging apparatus according to any one of Items 1 to 8.

(Item 10)
a step of detecting X-rays with an X-ray detector;
a step of performing a first X-ray imaging under a first X-ray imaging condition in which the non-subject area of the X-ray detection unit can detect the X-rays equal to or higher than the reference value required for imaging;
and performing a second X-ray imaging after the first X-ray imaging under a second X-ray imaging condition in which the subject area of the X-ray detection unit can detect the X-rays equal to or greater than the reference value. shooting method.

(Item 11)
The step of performing the second X-ray imaging controls at least one of a tube current of an X-ray source and a positional relationship between the X-ray source, the subject, and the X-ray detector in the optical axis direction of the X-rays. 11. An X-ray imaging method according to Item 10, including the step of changing the X-ray imaging conditions by doing.

(Item 12)
The step of performing the first X-ray imaging includes performing the first X-ray imaging with the X-ray source with a first tube current set,
12. An X-ray imaging method according to item 11, wherein the step of performing the second X-ray imaging includes performing the second X-ray imaging with the X-ray source in which a second tube current greater than the first tube current is set. .

(Item 13)
The step of performing the first X-ray imaging includes the X-ray source setting the first tube current such that the X-rays detected by the extra-subject area of the X-ray detection unit do not exceed the detection limit of the X-ray detection unit. including the step of performing the first radiography,
In the step of performing the second X-ray imaging, the X-rays detected by the non-object region of the X-ray detection unit exceed the detection limit of the X-ray detection unit, and the object region of the X-ray detection unit is X-ray imaging according to item 12, including the step of performing the second X-ray imaging with the X-ray source setting the second tube current such that the X-rays to be detected do not exceed the detection limit of the X-ray detection unit. Method.

(Item 14)
the step of detecting the X-rays with the X-ray detection unit includes detecting X-ray photons with the X-ray detection unit;
The step of performing the first X-ray imaging includes performing the first X-ray imaging conditions under the first X-ray imaging conditions under which the extra-subject area of the X-ray detection unit can detect the X-ray photons equal to or greater than a reference count required for imaging. 1 radiography,
In the step of performing the second X-ray imaging, the subject region of the X-ray detection unit performs the second X-ray imaging under the second X-ray imaging conditions under which the X-ray photons equal to or greater than the reference count can be detected. 14. The X-ray imaging method according to any one of items 10 to 13, comprising steps.

Reference Signs List 1 X-ray source 2 X-ray detection unit 4, 204 control unit 100, 200 X-ray imaging apparatus 110 subject

Claims (14)

an x-ray source;
an X-ray detector that detects X-rays emitted from the X-ray source;
a control unit that controls conditions for X-ray imaging of a subject by the X-ray source and the X-ray detection unit;
In the first X-ray imaging, the control unit sets a first X-ray imaging condition under which the region outside the object of the X-ray detection unit can detect the X-rays having a reference value or more required for imaging, and the first X-ray imaging In a second X-ray imaging performed after radiography, the subject area of the X-ray detection unit is configured to set a second X-ray imaging condition that allows detection of the X-rays equal to or greater than the reference value. photographic equipment. The control unit controls at least one of a tube current of the X-ray source and a positional relationship among the X-ray source, the subject, and the X-ray detection unit in the optical axis direction of the X-rays. , X-ray imaging apparatus according to claim 1, adapted to change the conditions of X-ray imaging. The control unit sets a first tube current to the X-ray source in the first X-ray imaging, and sets a second tube current larger than the first tube current in the second X-ray imaging. 3. An X-ray imaging device according to claim 2, adapted to be set to a source. In the first X-ray imaging, the control unit controls the X-ray source so that the X-rays detected by the extra-subject area of the X-ray detection unit do not exceed the detection limit of the X-ray detection unit. and in the second X-ray imaging, the X-ray detected by the extra-object area of the X-ray detection unit exceeds the detection limit of the X-ray detection unit, and the X-ray detection unit 4. The X-ray according to claim 3, wherein said X-ray source is configured to set said second tube current such that said X-rays detected by an object region do not exceed a detection limit of said X-ray detector. photographic equipment. 5. The X-ray imaging apparatus according to claim 4, wherein image data is acquired without using the detection result of the X-rays from the extra-subject area of the X-ray detection unit in the second X-ray imaging. . reconstructing the detection result of the X-rays by the X-ray detection unit in the first X-ray imaging and the second X-ray imaging based on the tube current and the imaging time of the first X-ray imaging and the second X-ray imaging The X-ray imaging apparatus according to any one of claims 2 to 5, wherein: By converting the detection result of the X-rays by the X-ray detection unit in another X-ray imaging based on the tube current and the imaging time of the last X-ray imaging of the second X-ray imaging, the first X-ray imaging 7. The X-ray imaging apparatus according to claim 6, configured to reconstruct the detection result of said X-rays by said X-ray detector in said second X-ray imaging. 8. The control unit according to any one of claims 1 to 7, wherein the control unit is configured to acquire the second X-ray imaging condition based on the detection result of the X-rays by the X-ray detection unit in the first X-ray imaging. 1. The X-ray imaging apparatus according to claim 1. The X-ray detection unit is configured to detect X-ray photons,
The control unit sets the first X-ray imaging conditions under which the extra-subject area of the X-ray detection unit can detect the X-ray photons equal to or greater than a reference count required for imaging in the first X-ray imaging. and in the second X-ray imaging, the subject region of the X-ray detection unit is configured to set the second X-ray imaging conditions under which the X-ray photons equal to or greater than the reference count can be detected. The X-ray imaging apparatus according to any one of claims 1-8. a step of detecting X-rays with an X-ray detector;
a step of performing a first X-ray imaging under a first X-ray imaging condition in which the non-subject area of the X-ray detection unit can detect the X-rays equal to or higher than the reference value required for imaging;
and performing a second X-ray imaging after the first X-ray imaging under a second X-ray imaging condition in which the subject area of the X-ray detection unit can detect the X-rays equal to or greater than the reference value. shooting method. The step of performing the second X-ray imaging controls at least one of a tube current of an X-ray source and a positional relationship between the X-ray source, the subject, and the X-ray detector in the optical axis direction of the X-rays. 11. The radiography method according to claim 10, comprising the step of changing radiography conditions by: The step of performing the first X-ray imaging includes performing the first X-ray imaging with the X-ray source with a first tube current set,
12. The radiography according to claim 11, wherein the step of performing the second radiography includes the step of performing the second radiography with the X-ray source in which a second tube current greater than the first tube current is set. Method. The step of performing the first X-ray imaging includes the X-ray source setting the first tube current such that the X-rays detected by the extra-subject area of the X-ray detection unit do not exceed the detection limit of the X-ray detection unit. including the step of performing the first radiography,
In the step of performing the second X-ray imaging, the X-rays detected by the non-object region of the X-ray detection unit exceed the detection limit of the X-ray detection unit, and the object region of the X-ray detection unit is 13. The X-ray according to claim 12, comprising the step of performing the second X-ray imaging with the X-ray source setting the second tube current such that the X-rays to be detected do not exceed the detection limit of the X-ray detection unit. shooting method. the step of detecting the X-rays with the X-ray detection unit includes detecting X-ray photons with the X-ray detection unit;
The step of performing the first X-ray imaging includes performing the first X-ray imaging conditions under the first X-ray imaging conditions under which the extra-subject area of the X-ray detection unit can detect the X-ray photons equal to or greater than a reference count required for imaging. 1 radiography,
In the step of performing the second X-ray imaging, the subject region of the X-ray detection unit performs the second X-ray imaging under the second X-ray imaging conditions under which the X-ray photons equal to or greater than the reference count can be detected. The radiographic method according to any one of claims 10 to 13, comprising steps.

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